1. Field of the Invention
The present invention relates to image display devices and modification methods performed by the same, and in particular to an image display device having a repairable pixel structure and a modification method performed by the same.
2. Description of the Related Art
Organic electro-luminescent (EL) displays including organic electro-luminescent elements (hereinafter referred to as organic EL elements) are known as image display devices including current-driven luminescent elements. The organic EL displays are attracting attention as a candidate for next-generation flat panel displays (FPDs) because they are viewable at wide angles and consume a small amount of power.
Usually, organic EL elements included in pixels are arranged in a matrix pattern. For example, in active-matrix organic EL displays, thin-film transistors (TFTs) are provided at intersections of scanning lines and data lines, and each TFT is connected with a capacitive element (capacitor) and the gate of a driving transistor. The TFT is turned on through a selected scanning line to allow a data signal to be provided to the driving transistor and the capacitive element through a corresponding data line so that the driving transistor and the capacitive element control the timing when the organic EL element produces luminescence. With this configuration of the pixel driving circuit, the active-matrix organic EL displays can cause the organic EL elements to keep producing luminescence until next scanning (selection), and thus there is no reduction in the display luminance even when the duty ratio increases. However, as typified by the active-matrix organic EL displays, when the complexity of the driving circuit configuration of the luminescent pixels increases or when the number of luminescent pixels increases, electrical troubles, such as a short circuit and/or an open circuit of circuit elements and wires, are more likely to occur during a manufacturing process which requires fine processing.
With organic EL panels, in particular, the capacitive elements included in the pixel driving circuits have a relatively wide element area. Consequently, the capacitive elements are susceptible to a particle or the like present between electrodes, thereby causing a higher percent defective of pixels through a short circuit.
Meanwhile, there is a method proposed for repairing a defective luminescent pixel after forming pixel driving circuit elements and wires. In order to repair a defective luminescent pixel which has become a bright point in a constant luminescent status due to a short circuit of a circuit element or the like, Patent Reference 1 (Japanese Unexamined Patent Application Publication No. 2008-203636) provides, in all the luminescent pixel regions, a non-overlapping portion connected to other conductive portions and wires with some distance therefrom. To repair a defective luminescent pixel, the non-overlapping portion is disconnected by laser irradiation. With this, transmission of electric signals to the defective luminescent pixel is blocked. Moreover, the defective luminescent pixel becomes a dark point with no damage from the laser irradiation.
Furthermore, in Patent Reference 2 (Japanese Unexamined Patent Application Publication No. 2007-66904), a pixel electrode formed in a luminescent region of each luminescent pixel is provided by connecting cells, so that by disconnecting a cell connection with a laser, only the defective luminescent cell is electrically insulated and becomes a dark point.